Slurry hydrocracking (SHC) is used for the upgrading of heavy hydrocarbon feedstocks. In SHC, these feedstocks are converted in the presence of hydrogen and solid catalyst particles (e.g., as a particulate metallic compound such as a metal sulfide) in a slurry phase. Representative slurry hydrocracking processes are described, for example, in U.S. Pat. No. 5,755,955 and U.S. Pat. No. 5,474,977.
Desirably, SHC would run at about 90% conversion of 524+° C. (975+° F.) hydrocarbons or higher. Higher conversion is always preferred with higher product yield and less residue left unconverted. However, higher conversion levels in SHC are always obtained at the expense of a greater risk of precipitating asphaltenes present in the heavy hydrocarbon feedstock coke precursors or coke. Although coke formation can be controlled using a catalyst with higher activity, higher catalyst loading, higher reactor pressure, or lower reactor temperature, frequently the coke formation reaction under SHC conditions is not controlled effectively by applying one or a combination of these methodologies for both technical and economic reasons.
Frequently, SHC involves the use of less expensive catalyst, or a lower dosage when using a more expensive catalyst, which would preferably be in unsupported metal form. Asphaltene conversion in SHC is therefore frequently found to be limited by the effectiveness of the catalyst applied under SHC conditions. Ebullated bed hydrocracking (EBHC) is also used to upgrade heavy hydrocarbon feed often using more active catalyst, e.g., a mixture of at least one Group VIII metal (preferably cobalt and/or nickel) and at least one Group VI metal (preferably molybdenum and/or tungsten) on a high surface area support material, preferably alumina. The higher activity catalyst in EBHC allows for effective hydrogenation of the feed at a lower severity; however, EBHC conversion is limited due to the intrinsically high fouling propensity when high conversion is pursued in a single step.
Therefore, there is a need for a process in which heavy hydrocarbons are converted or upgraded with improved efficiency and conversion.